[tor-bugs] #24688 [Core Tor/Tor]: timing wheels should use 32-bit math on 32-bit platforms

Tor Bug Tracker & Wiki blackhole at torproject.org
Tue Apr 17 10:59:52 UTC 2018


#24688: timing wheels should use 32-bit math on 32-bit platforms
-------------------------------------------------+-------------------------
 Reporter:  nickm                                |          Owner:  nickm
     Type:  defect                               |         Status:
                                                 |  merge_ready
 Priority:  Medium                               |      Milestone:  Tor:
                                                 |  0.3.4.x-final
Component:  Core Tor/Tor                         |        Version:
 Severity:  Normal                               |     Resolution:
 Keywords:  cpu, 32-bit, timing,                 |  Actual Points:
  034-triage-20180328, fast-fix                  |
Parent ID:                                       |         Points:
 Reviewer:  asn                                  |        Sponsor:
                                                 |  Sponsor8-can
-------------------------------------------------+-------------------------
Changes (by asn):

 * status:  needs_review => merge_ready


Comment:

 Patch seems like an OK change if we have hints it can improve performance.
 However, I didn't manage to find any other tickets with profiler outputs
 etc.

 Anyhow, I guess the most important thing is to check for correctness. I
 couldn't do that with code review because the `timeouts.c` codebase is
 very intense. However, I did the following:

 - Read the timeouts documentation and ensured that `WHEEL_BIT` is
 configurable. Also we are already configuring `WHEEL_NUM`.
 - Cloned official timeouts codebase from
 `https://github.com/wahern/timeout` and changed the `WHEEL_BIT` variable
 and ran the unittests. Passed fine.
 - Tested that the `WHEEL_BIT` variable gets set correctly in the Tor
 codebase when the #ifdef passes.
 - Tested that a Tor client works fine with `WHEEL_BIT` set to 5.

 I think that looks good enough.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/24688#comment:7>
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